1. Field of the Invention
The invention relates to an image forming apparatus adopting an electrophotographic process or an electrostatic recording process, and particularly to an image forming apparatus such as a copying machine, a printer or a facsimile apparatus. More particularly, it relates to an image forming apparatus such as a copying machine, a printer or a facsimile apparatus capable of forming a full-color image.
2. Description of Related Art
In an image forming portion in an image forming apparatus such as a copying machine, a photosensitive member which is an image bearing member is charged by a charging apparatus, and is exposed to the image of an original at an exposure position by an exposing optical system to thereby form an electrostatic latent image on the peripheral surface of the photosensitive member, and this electrostatic latent image is developed by a developing apparatus to thereby form a developer image (toner image), and this toner image is transferred to a transferring material by the application of a voltage by a transferring apparatus, and the photosensitive member after the transfer is cleaned by a cleaning apparatus, whereafter exposure before charging is effected to thereby remove any residual charges on the photosensitive member, and the above-described process is repeated again to thereby effect image forming.
There has also been proposed an image forming apparatus which is provided with a plurality of photosensitive members, charging apparatuses and developing apparatuses and repeats the above-described image forming process a plurality of times to thereby form a full-color image.
Further, in the above-described image forming apparatus for forming a full-color image, it has heretofore been proposed to provide a plurality of developer carrying members (hereinafter referred to as the developing sleeves) in the developing apparatuses.
In this case, the developing sleeves are disposed with a predetermined clearance relative to the photosensitive members, but it is possible to form images of high definition at a high speed without greatly increasing the peripheral speed of the developing sleeves.
Also, in the black-and-white image forming apparatus of Japanese Patent Application Laid-Open No. 2000-147900 which has a developing device provided with a plurality of developing sleeves and fixedly disposed around a photosensitive member, there is proposed a method of pressing one developing sleeve against the photosensitive member with the other developing sleeve as a fulcrum.
The above-described full-color image forming apparatus, however, tends to become bulky, and has posed a problem in this point. That is, neither of the higher speed and higher quality of image and the downsizing of the image forming apparatus could be made compatible.
Also, it has been found by our studies that when supposing a construction in which a developing device provided with a plurality of developing sleeves is moved to a developing position by a rotary type developing apparatus to thereby effect developing, it is considered that when the rotary type developing apparatus is rotated, the developing sleeves interfere with the photosensitive member and therefore, it is difficult to highly accurately dispose the plurality of developing sleeves and the photosensitive member in proximity to each other.